Yesterday I got reminded that something was wrong with my system. After going into /tmp to temporarily clone a repository, it appeared that the directory was not wiped on reboot. I just thought it was some weird bug and moved on.
Today the situation didn't change, so I went deeper. By checking some init scripts, I found the following in /etc/init.d/bootmisc:
cleanup_tmp_dir()
{
# ...
cd "$dir" || return 1
if yesno $wipe_tmp; then
ewarn "The wipe_tmp setting has been enabled in /etc/conf.d/bootmisc."
ewarn "This setting is no longer recommended by Alpine due to reported"
ewarn "data loss incidents relating to it."
ewarn "See alpine/aports#13070 for more information."
ebegin "Wiping $dir directory"
# ...
else
# ...
fi
}
In short: the wipe_tmp option was disabled because it ran 'rm -rf' on the entire disk.
Initially wiping /tmp appeared weird, because it was not supposed to be even written to disk. But it is by default.
This brings to the feature in Linux called 'tmpfs'. It's a non-persistent filesystem that lives in memory and thus is destroyed on reboot. This is exactly what I want for /tmp!
To enable it, add the following to /etc/fstab and reboot. Just make sure that old /tmp is wiped before because it won't be easily accessible.
tmpfs /tmp tmpfs mode=1777,nosuid,nodev,strictatime
It has a special type 'tmpfs', mounted on /tmp with some options: set mode to sticky + read-write-execute for all users, disable setuid binaries, disable block devices, and allow to request access time updates.
Note: sticky bit only allows the owner or root to move or delete their files.
It's also possible to dynamically mount tmpfs by using mount:
# mount \ -t tmpfs \ -o mode=1777,nosuid,nodev,strictatime \ tmpfs /my-custom-tmp
When using 'tmpfs' it should be considered that the system has enough RAM to handle everything there. So, it's not recommended to build large trees in /tmp because it may lock up or crash with out of memory error.
That's it for today, hope you're having a great day :)
"Using tmpfs" was written on October 17, 2021